One of my favorite artists is urban sketcher/architect Liz Steel. She's Australian and very active in blogging her sketches, techniques, and product reviews in addition to teaching classes. I highly recommend you check her out! I recently purchased her latest read, 5-Minute Sketching--Architecture: Super-quick Techniques for Amazing Drawings, and love it! It's very helpful! i really like all the examples and hope to put her techniques into practice once the weather breaks.
Liz's blog has all kind of inspiration! I really enjoy her coffee sketches and seeing what's in her watercolor palette. Recently, she posted sketches from her trip to New Zealand. Stop by her site...but make sure you have plenty of time! http://www.lizsteel.com/